E. Zilkha

EFFECT OF HÆMATOCRIT ON CEREBRAL BLOOD-FLOW IN MAN

Abstract Cerebral blood-flow (C.B.F.) was measured in 38 patients with haematocrit values (Hct) in the range 0·47-0·53 and was found to be significantly lower than in 43 patients with Hct in a lower range (0·36-0·46). After reduction of Hct in the higher Hct group by venesection, flow increased by a mean of 50%. This improvement in flow was largely due to a reduction in viscosity. Hct around the generally accepted upper limit of normal may be an important factor in the causation of occlusive vascular disease.

CEREBRAL BLOOD-FLOW AND VISCOSITY IN RELATIVE POLYCYTHÆMIA

Abstract Cerebral blood flow (CBF), red-cell mass, and plasma volume were measured in 39 patients with venous haematocrit values in the range 0·47-0·58. Patients with true polycythaemia were thus excluded. The 39 patients studied fell into two groups—those with a measured red-cell mass in the high-normal range and those with normal red-cell-mass values but reduced plasma-volume values (the relative-polycythaemia, low-plasma-volume group). The mean CBF was low in both the high-normal red-cell-mass (HNRCM) group (45·8 ml/100 g/min) and low-plasma-volume (LPV) group (48·8 ml/100 g/min). The haematocrit in the HNRCM group was 0·504 and in the LPV group 0·513. In a control group of subjects with a mean haematocrit of 0·421 CBF was 68·6 ml/100 g/min. Venesection was associated with a significant rise in CBF in both groups of patients—to 59·7 ml/100 g/min in the HNRCM group and 65·0 ml/100 g/min in the LPV group. Whole-blood viscosity fell significantly in both groups. Both groups demonstrated significant inverse relationships between CBF and haematocrit and between CBF and blood viscosity.

Measurement of regional cerebral blood volume by computerized axial tomography.

Computerized tomography has been used for the estimation of regional cerebral blood volume in a group of 18 patients. Sodium iothalamate was injected intravenously (1.75 ml/kg) to increase the absorption of x-rays in the cerebral circulation. A mean value of 5.7 ml/100 g was found for the cortex and 5.1 for tha thalamus.

An intravenous 133xenon clearance technique for measuring cerebral blood flow.

An intravenous 133Xe clearance technique for measuring cerebral blood flow (CBF) is described. Results obtained compared well with those using the intracarotid 133Xe technique. The reproducibility of the method was checked by repeating measurements within a few hours in 14 patients, when no significant overall change occurred, and after some days in 23 patients when a mean fall in flow of 8% was observed. CBF was measured in 52 control subjects. The mean fast component flow (Ff) was 68.6 ml/100 g/min (SD 11.3). No difference between the two hemispheres was found. Flow was confirmed to be higher anteriorly in the cerebral hemispheres. A significant inverse correlation was found between CBF and age.

Computer subtraction in regional cerebral blood-volume measurements using the EMI-Scanner

A computerized subtraction technique has been described to measure regional cerebral blood volume (rCBV) using the EMI-Scanner in a group of 13 patients. Sodium iothalamte was injected intravenously (1-75 ml./kg) to increase the absorption of X rays in the cerebral circulation. Significant regional differences in CBV were shown, values in the frontal and temporal regions being lower than the mean hemisphere value (4-9 +/- 0-7) and higher in the occipital region. The left hemisphere showed a significantly higher CBV when compared with the right. Measurements of CBV in the cortex showed no regional variation, but the mean cortical value of 6-0 +/- 1-8 was significantly higher than the hemisphere mean.

Cerebral Blood Flow Studies in Patients with Cluster Headache

SYNOPSIS

Viscosity, cerebral blood flow and haematocrit in patients with paraproteinaemia

It has been suggested that blood viscosity is involved in the control of cerebral blood flow (CBF) (Thomas et al. 1977a, b, Humphrey et al. 1979). CBF, using the intravenous Xenon133 technique, blood viscosity and haematocrit were measured in 21 patients with elevated viscosity due to paraproteinaemia and found to be the same as in normal subjects. However, the paraproteinaemic patients were anaemic with a mean haematocrit of 0.342. This degree of anaemia would normally be associated with a high CBF.

Cerebral blood flow, haematocrit and viscosity in subjects with a high oxygen affinity haemoglobin variant

The cerebral blood flow is low in primary polycythaemia, and it has been suggested that this is due to the increase in viscosity which accompanies the elevated haematocrit. In the present study cerebral blood flow has been measured by a non‐invasive 133Xenon technique in six subjects with an elevated haematocrit secondary to a haemoglobin variant with increased oxygen affinity. Flow was significantly higher than normal and 81 % higher than in 11 subjects of comparable age, matched for haematocrit and viscosity, but without the haemoglobin variant. In patients with this unusual type of polycythaemia, cerebral blood flow is high despite the elevated blood viscosity and the implications of these results are discussed.

Cerebral blood flow after surgery for recent subarachnoid haemorrhage

243 measurements of cerebral blood flow by a noninvasive 133Xe clearance technique have been made in 45 patients undergoing surgery for a recently ruptured cerebral aneurysm. Two groups of patients have been defined by the presence or absence of a postoperative rise in cerebral blood flow which showed a significant correlation with level of consciousness after operation.

Measurement of regional cerebral blood volume using the EMI 1010 scanner

Regional cerebral blood volume (rCBV) was measured in 14 patients with normal CT scans. An EMI CT 1010 scanner was used in combination with a computer subtraction technique. The mean CBV in the cortex was 5.0 ml/100 ml of tissue and 2.2 in the white matter. Regional differences were not significant and no difference was found between the right and left hemispheres.